Galaxies

[Wiccan_Child]

Uh... I'm not sure I get this. It sounds a bit like my fingers must be temporally distinct from my toes just because they aren't exactly identical. Or do you just mean single-component systems like particles?

I mean that if a system undergoes a change, then time has been shown to exist. The system naturally incorporates spatial displacement.

But particles aren't really indivisible either (though for all I know, maybe a photon is).

As far as we can tell, there are particles that are indivisible (e.g., the electron, the various quarks, the photon, etc). They are truly point-like.

My poor little head is spinning.

But like an electron, it's not really spinning .

 

[Naraoia]

But like an electron, it's not really spinning .

And unlike an electron, it doesn't have to not-really-spin around twice to show the same face

 

[Chesterton]

So why does light move anyway? What makes for the propulsion?

Also, if I shine a light into an aquarium full of water - passing through the air it goes one speed, then passing through the glass and water it slows down, but then upon exiting the aquarium and moving through the air on the other side, I assume it speeds back up to air speed? Is that so, and if so, how does it regain the speed?

 

[maybenotcrazy]

So why does light move anyway? What makes for the propulsion?

Also, if I shine a light into an aquarium full of water - passing through the air it goes one speed, then passing through the glass and water it slows down, but then upon exiting the aquarium and moving through the air on the other side, I assume it speeds back up to air speed? Is that so, and if so, how does it regain the speed?

All I can tell you is that light always travels at the speed of light in a vacuum without any propulsion. This is just a fact of nature. When it enters something it slows down as a result of refraction. The wave peaks and troughs become more distant from one another so the time between them decreases. this is probably due in my stupid opinion to the electromagnetic nature of light. It interacts with a medium's particles which have electric charge and magnetic pull which cause, as the wave enters the medium the wave to be stretched. The speed of a wave is the time it takes for a trough or peak to travel one wavelength or equivalently, the distance between the peaks or troughs divided by the duration of one cycle of the wave. Think of what I was saying about electromagnetic fields. if you have two ropes connected to each other of different thickness (and density) the
lighter rope will have a faster wave travel along it than the heavier one then a lighter rope connected to that would resume speed at a lower amplitude... of course reflection complicates things too... This is refraction. The charges of particles cause them to be moved by the particle dissipating some of the energy of the light in the dense medium adding "weight" to the rope as it were. When light exits, much of its volume is dissipated by this process but the energy density per unit time or flux density remains the same so that light exiting regains its frequency albeit at a lower total energy (because so much energy was lost in the object) So the slowing of light means a loss of energy and it is continuously lost because in between particles there is a vacuum and light keeps reemerging from and reentering the influence of electric disturbances so that with each disturbance the energy lowers more without slowing the light down continuously. If it were a continuous drain in energy without re"acceleration" light would continue to slow down and stop but because there is space in a material even if it is pretty electron dense light continues to propagate. Of course this is a classical explanation. I don't really understand quantum so I can't tell you about that.

You might find interesting the fact that polarized light is tilted in solutions of assymetric molecules. The explanation is complicated and beyond my intuition's capacity.

 

[Wiccan_Child]

So why does light move anyway? What makes for the propulsion?

It is massless and has energy, so it therefore has momentum. Classically, it is a self-inducing electric and magnetic fields (an electric field creates a magnetic field, and a magnetic field creates an electric field):

Classical mechanics is wrong, but it makes intuitive sense, so it might help to think of it this way.

Also, if I shine a light into an aquarium full of water - passing through the air it goes one speed, then passing through the glass and water it slows down, but then upon exiting the aquarium and moving through the air on the other side, I assume it speeds back up to air speed? Is that so, and if so, how does it regain the speed?

It is an illusion: light travels at the same speed no matter what medium it is in. The reason it seems to slow down is because it is constantly being absorbed and reemitted by the particles of the medium, and there is a short delay between the two. So while it travels at c, it 'stops' for a brief period every time it encounters a particle. That's why it takes longer to travel through a medium than through empty space.

This is also evident in the theory of special relativity: it's fundamental assumption is that light always travels at c, regardless of what you (the observer) is doing.

Finally, there is a phenomenon called Čerenkov radiation, where electrons are moving faster than light:

Eerie.

 

[Chesterton]

That's why it takes longer to travel through a medium than through empty space.

Isn't "takes longer to travel" synonymous with "slows down"?

This is also evident in the theory of special relativity: it's fundamental assumption is that light always travels at c, regardless of what you (the observer) is doing.

But I've always heard "light always travels at c in a vacuum", and less than c through mediums. No?

 

[ragarth]

So why does light move anyway? What makes for the propulsion?

Also, if I shine a light into an aquarium full of water - passing through the air it goes one speed, then passing through the glass and water it slows down, but then upon exiting the aquarium and moving through the air on the other side, I assume it speeds back up to air speed? Is that so, and if so, how does it regain the speed?

Light is a massless particle. in special relativity (e=mc^2) it's: 0=0c^2, so it's energy is 0 eV. It has a virtual mass due to it's velocity, but this virtual mass does not effect it's capacity to travel at the speed of light.

This 0 mass and energy makes photons rather binary, they're either traveling at maximum velocity (c) or minimum velocity (0), and since brownian motion makes any particle above a temperature of 0 kelvin move, and since 0 kelvin is impossible to reach, light cannot have a velocity of 0 so it must always travel at a velocity of c.

 

[maybenotcrazy]

I know the old adage about arguing on the internet, but I love this, it is tremendously interesting and stimulating. I never thought I'd get a chance to write an essay on light but here I am. Dumb as ever proving I have no brain.

Light is a massless particle. in special relativity (e=mc^2) it's: 0=0c^2, so it's energy is 0 eV. It has a virtual mass due to it's velocity, but this virtual mass does not effect it's capacity to travel at the speed of light.

This 0 mass and energy makes photons rather binary, they're either traveling at maximum velocity (c) or minimum velocity (0), and since brownian motion makes any particle above a temperature of 0 kelvin move, and since 0 kelvin is impossible to reach, light cannot have a velocity of 0 so it must always travel at a velocity of c.

Uh. Ragarth. I'm not a physicist, but would it be appropriate to say that light has a temperature? I know you've heard of color temperature but that is not the same thing. Light is energy, not matter and brownian motion is a random walk associated with matter and classical physics. It may have a quantum basis but it is less specific than that.

As for the photon theory of motion, I will try to explain it intuitively without any advanced concepts. First of all the direction in which a photon will be emitted by an atom is random. When the quantized energy level of an atom is decreased, a photon is emitted because the electron loses potential energy by entering a less energetic orbital (or simplistically, comes closer to the nucleus). Momentum is also lost because the electron slows down. This momentum is always enough to give the photon momentum (which is not mass related but related to the photon's ability to cause a force to be exerted on something, so it is like the force of the electron slowing down is projected in space as a "particle of force. or a momentum." Momentum is not mass times velocity in this case but the potential m(delta)v that would be exerted on a particle if it experienced the electromagnetic field caused by the photon. The photon travels at the speed of light for reasons I don't know but travels onward in the random direction it left an atom by for the same reason a disturbance in a cloth would propagate, or a wave in the ocean. The maxwell equations describe why the propagation occurs (and I will explain intuitively!!!)
1

Unintelligible explanation:
The first one most basically says in words: An electric field's curl is determined by the rate of change of the magnetic field. The upside down triangle with the X next to it describes the "curl" in the electric field or the vector perpendicular to the tangent line to the electric field, specifically the perpendicular that is perpendicular to the radius of a circle that fits the curvature of the field line at a given point OK!!!!???? Am I boring you to tears? GOOD!!!
Intelligible: The above means that there is an electric field that exists with a certain "curvature" in terms of direction in which the field points that is determined by the rate of change (or speed with which) a magnetic field changes in time. There is also an equation like this for magnetism. So basically this means that if there is a distortion in the electric field somewhere, caused by a photon this is going to elicit by law, a changing magnetic field which will elicit a change in the electric field ad nauseum. A photon is the quantum of energy and momentum that is embodied by this disturbance in the magnetic field and that is how a photon gets its motion. By being affiliated with an electric and magnetic field....


Just for kicks, the maxwell equations (to teach me, I know you don't care!)

There are other equations too that give rules for the electric and magnetic fields to follow. Obviously the lines don't converge

unless there is a charge in space. that's the rho. So the angle of the change in direction of force vectors to the x y and z axes remains constant unless there is a charge, i.e. if there is no charge, the divergence is zero or there is no rate of change of direction of force vectors.

there is an equation that says the divergence of the magnetic field is always zero (there are no magnetic monopoles!!!! it says)
Then there is the analogous equation to the first one I gave.
All this says that waves are possible and do propagate at the speed of light.

Obviously I'm wrong somewhere but that really was a fun way to spend my half hour!!!!

 

[Wiccan_Child]

Isn't "takes longer to travel" synonymous with "slows down"?

No. "Takes longer" can imply either "slows down" or "travels further". If I travel at 50mph along a stretch of road, it will take me a certain amount of time. However, if I weave back and forth across the road, it will take me much longer to reach my destination. Why? Because I've travelled further.

But I've always heard "light always travels at c in a vacuum", and less than c through mediums. No?

No. It effectively slows down, but it actually does not. It is far easier to model light slowing down in media, but that isn't what actually happens.

 

[Wiccan_Child]

Uh. Ragarth. I'm not a physicist, but would it be appropriate to say that light has a temperature? I know you've heard of color temperature but that is not the same thing. Light is energy, not matter and brownian motion is a random walk associated with matter and classical physics. It may have a quantum basis but it is less specific than that.

The photon is matter.

As for the photon theory of motion, I will try to explain it intuitively without any advanced concepts. First of all the direction in which a photon will be emitted by an atom is random. When the quantized energy level of an atom is decreased, a photon is emitted because the electron loses potential energy by entering a less energetic orbital (or simplistically, comes closer to the nucleus). Momentum is also lost because the electron slows down. This momentum is always enough to give the photon momentum (which is not mass related but related to the photon's ability to cause a force to be exerted on something, so it is like the force of the electron slowing down is projected in space as a "particle of force. or a momentum." Momentum is not mass times velocity in this case but the potential m(delta)v that would be exerted on a particle if it experienced the electromagnetic field caused by the photon. The photon travels at the speed of light for reasons I don't know but travels onward in the random direction it left an atom by for the same reason a disturbance in a cloth would propagate, or a wave in the ocean.

The photon is not a wave in a medium. The idea of a luminiferous aether has long since been disproven. The photon propagates for the same reason an electron propagates: because it has kinetic energy, and because there is no net force acting on it.

The maxwell equations describe why the propagation occurs (and I will explain intuitively!!!)
1

Unintelligible explanation:
The first one most basically says in words: An electric field's curl is determined by the rate of change of the magnetic field. The upside down triangle with the X next to it describes the "curl" in the electric field or the vector perpendicular to the tangent line to the electric field, specifically the perpendicular that is perpendicular to the radius of a circle that fits the curvature of the field line at a given point OK!!!!???? Am I boring you to tears? GOOD!!!

Eh, almost. The curl of a field is a vector that is perpendicular to the direction in which that field curls.

In this case, the curl of the field is along the z-axis.

So Maxwell's equation is saying that the magnetic field changes in such a way that it increases in a direction perpendicular to the 'swirl' of the electric field.

But no one bothers with curl. It's the unwanted child of electrodynamics.

 

[Chesterton]

No. "Takes longer" can imply either "slows down" or "travels further". If I travel at 50mph along a stretch of road, it will take me a certain amount of time. However, if I weave back and forth across the road, it will take me much longer to reach my destination. Why? Because I've travelled further.

Yeah, I got that after I read your initial answer again. Thanks.

mediums

media

And I had to do that in front of an Englishman.